The desire of computer users to become more mobile has led to increased use of server-side data storage, including web-based data storage. According to typical server-side storage arrangements, a service provider (e.g., a company or other organization, a commercial provider, etc.) implements one or more network-accessible hosts. Each host usually comprises data storage hardware and one or more servers for administering the hardware. Users of the service are able to access the hosts over the network to upload and download data files. The network may be a local area network (LAN) or a wide area network (WAN), such as the Internet. Typically, the users can access the central data store from multiple computer devices, and often from any computer device having the appropriate client software and the ability to communicate on the network.
Although server-side data storage generates conveniences for computer users, it also presents new risks and concerns. Data security is one significant concern. Because the service provider, and not the users, are in control of the data, users must rely on the service provider to maintain data security. Some users have addressed this concern by encrypting files before uploading the files to a host. This, however, requires that the entire file be transferred from client to host and back again every time that it is modified. In addition, when files are encrypted to a host, the host cannot index the files for easy retrieval by the clients/users.